/**
 * Copyright (C) 2002-2015   The FreeCol Team
 * <p>
 * This file is part of FreeCol.
 * <p>
 * FreeCol is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 * <p>
 * FreeCol is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * <p>
 * You should have received a copy of the GNU General Public License
 * along with FreeCol.  If not, see <http://www.gnu.org/licenses/>.
 */

package net.sf.freecol.server.ai.mission;

import java.util.logging.Logger;

import javax.xml.stream.XMLStreamException;

import net.sf.freecol.common.io.FreeColXMLReader;
import net.sf.freecol.common.io.FreeColXMLWriter;
import net.sf.freecol.common.model.Ability;
import net.sf.freecol.common.model.Colony;
import net.sf.freecol.common.model.IndianSettlement;
import net.sf.freecol.common.model.Location;
import net.sf.freecol.common.model.Direction;
import net.sf.freecol.common.model.PathNode;
import net.sf.freecol.common.model.Player;
import net.sf.freecol.common.model.Settlement;
import net.sf.freecol.common.model.Tension;
import net.sf.freecol.common.model.Tile;
import net.sf.freecol.common.model.Unit;
import net.sf.freecol.common.model.pathfinding.CostDecider;
import net.sf.freecol.common.model.pathfinding.CostDeciders;
import net.sf.freecol.common.model.pathfinding.GoalDecider;
import net.sf.freecol.common.model.pathfinding.GoalDeciders;
import net.sf.freecol.common.util.LogBuilder;
import net.sf.freecol.server.ai.AIMain;
import net.sf.freecol.server.ai.AIMessage;
import net.sf.freecol.server.ai.AIUnit;


/**
 * Mission for controlling a scout.
 */
public class ScoutingMission extends Mission
{

    private static final Logger logger = Logger.getLogger( ScoutingMission.class.getName( ) );

    /** The tag for this mission. */
    private static final String tag = "AI scout";

    /**
     * The target for this mission.
     * - A tile with an LCR
     * - A native settlement to talk to the chief of
     * - A player colony to retarget from
     * - An unexplored tile
     */
    private Location target;


    /**
     * Creates a mission for the given <code>AIUnit</code>.
     *
     * @param aiMain The main AI-object.
     * @param aiUnit The <code>AIUnit</code> this mission is created for.
     * @param target The target <code>Location</code>.
     */
    public ScoutingMission( AIMain aiMain, AIUnit aiUnit, Location target )
    {
        super( aiMain, aiUnit, target );
    }

    /**
     * Creates a new <code>ScoutingMission</code> and reads the given element.
     *
     * @param aiMain The main AI-object.
     * @param aiUnit The <code>AIUnit</code> this mission is created for.
     * @param xr The input stream containing the XML.
     * @throws XMLStreamException if a problem was encountered during parsing.
     * @see net.sf.freecol.server.ai.AIObject#readFromXML
     */
    public ScoutingMission( AIMain aiMain, AIUnit aiUnit,
                            FreeColXMLReader xr ) throws XMLStreamException
    {
        super( aiMain, aiUnit );

        readFromXML( xr );
    }


    /**
     * Does a supplied unit have horses?
     *
     * @param aiUnit The scout <code>AIUnit</code> to check.
     * @return True if the scout has horses.
     */
    private static boolean canScoutNatives( AIUnit aiUnit )
    {
        return aiUnit.getUnit( )
                .hasAbility( Ability.SPEAK_WITH_CHIEF );
    }

    /**
     * Extract a valid target for this mission from a path.
     *
     * @param aiUnit A <code>AIUnit</code> to perform the mission.
     * @param path A <code>PathNode</code> to extract a target from,
     *     (uses the unit location if null).
     * @return A target for this mission, or null if none found.
     */
    public static Location extractTarget( AIUnit aiUnit, PathNode path )
    {
        if ( path == null ) return null;
        final Location loc = path.getLastNode( ).getLocation( );
        return ( loc == null ) ? null
                : ( invalidSettlementReason( aiUnit, loc.getSettlement( ) ) == null )
                ? loc.getSettlement( )
                : ( invalidTileReason( aiUnit, loc.getTile( ) ) == null )
                ? loc.getTile( )
                : null;
    }

    /**
     * Evaluate a potential scouting mission for a given unit and
     * path.
     *
     * @param aiUnit The <code>AIUnit</code> to do the mission.
     * @param path A <code>PathNode</code> to take to the target.
     * @return A score for the proposed mission.
     */
    public static int scorePath( AIUnit aiUnit, PathNode path )
    {
        Location loc = ( path == null ) ? null : extractTarget( aiUnit, path );
        return ( loc instanceof Colony )
                ? 12 / ( path.getTotalTurns( ) + 1 )
                : ( loc instanceof IndianSettlement )
                ? 2000 / ( path.getTotalTurns( ) + 1 )
                : ( loc instanceof Tile )
                ? ( ( ( ( Tile ) loc ).hasLostCityRumour( ) )
                ? 1000 / ( path.getTotalTurns( ) + 1 )
                : 50 / ( path.getTotalTurns( ) + 1 ) )
                : Integer.MIN_VALUE;
    }

    /**
     * Gets a <code>GoalDecider</code> for finding the best colony
     * <code>Tile</code>, optionally falling back to the nearest colony.
     *
     * @param aiUnit The <code>AIUnit</code> that is searching.
     * @param deferOK Enable colony fallback.
     * @return A suitable <code>GoalDecider</code>.
     */
    private static GoalDecider getGoalDecider( final AIUnit aiUnit,
                                               boolean deferOK )
    {
        GoalDecider gd = new GoalDecider( )
        {
            private PathNode bestPath = null;
            private int bestValue = Integer.MIN_VALUE;

            @Override
            public PathNode getGoal( ) { return bestPath; }

            @Override
            public boolean hasSubGoals( ) { return true; }

            @Override
            public boolean check( Unit u, PathNode path )
            {
                Location loc = extractTarget( aiUnit, path );
                if ( loc instanceof IndianSettlement
                        || loc instanceof Tile )
                {
                    int value = scorePath( aiUnit, path );
                    if ( bestValue < value )
                    {
                        bestValue = value;
                        bestPath = path;
                        return true;
                    }
                }
                return false;
            }
        };
        return ( deferOK ) ? GoalDeciders.getComposedGoalDecider( false, gd,
                                                                  GoalDeciders.getOurClosestSettlementGoalDecider( ) )
                : gd;
    }

    /**
     * Finds a suitable scouting target for the supplied unit.
     *
     * @param aiUnit The <code>AIUnit</code> to execute this mission.
     * @param range An upper bound on the number of moves.
     * @param deferOK Enables deferring to a fallback colony.
     * @return A path to the new target, or null if none found.
     */
    public static PathNode findTargetPath( AIUnit aiUnit, int range,
                                           boolean deferOK )
    {
        if ( invalidAIUnitReason( aiUnit ) != null ) return null;
        final Unit unit = aiUnit.getUnit( );
        final Location start = unit.getPathStartLocation( );
        final Unit carrier = unit.getCarrier( );
        final GoalDecider gd = getGoalDecider( aiUnit, deferOK );
        final CostDecider standardCd = CostDeciders.avoidIllegal( );

        // Can the scout legally reach a valid target from where it
        // currently is?
        return unit.search( start, gd, standardCd, range, carrier );
    }

    /**
     * Finds a suitable scouting target for the supplied unit.
     * Falls back to the best settlement if a path is not found.
     *
     * @param aiUnit The <code>AIUnit</code> to test.
     * @param range An upper bound on the number of moves.
     * @param deferOK Enables deferring to a fallback colony.
     * @return A <code>PathNode</code> to the target, or null if none found.
     */
    public static Location findTarget( AIUnit aiUnit, int range,
                                       boolean deferOK )
    {
        PathNode path = findTargetPath( aiUnit, range, deferOK );
        return ( path != null ) ? extractTarget( aiUnit, path )
                : Location.upLoc( findCircleTarget( aiUnit,
                                                    getGoalDecider( aiUnit, deferOK ), range * 3, deferOK ) );
    }

    /**
     * Prepare a unit for this mission.  Allow even experts to proceed
     * even if not mounted.
     *
     * @param aiUnit The <code>AIUnit</code> to prepare.
     * @return A reason why the unit can not perform this mission, or null
     *     if none.
     */
    public static String prepare( AIUnit aiUnit )
    {
        String reason = invalidReason( aiUnit );
        return ( reason != null ) ? reason
                : ( canScoutNatives( aiUnit )
                || aiUnit.equipForRole( aiUnit.getUnit( ).getSpecification( )
                                                .getScoutRole( ) )
                || aiUnit.getUnit( ).hasAbility( Ability.EXPERT_SCOUT ) ) ? null
                : "unit-unprepared-to-SCOUT";
    }

    /**
     * Why would this mission be invalid with the given unit.
     *
     * @param aiUnit The <code>AIUnit</code> to check.
     * @return A reason why the mission would be invalid with the unit,
     *     or null if none found.
     */
    private static String invalidMissionReason( AIUnit aiUnit )
    {
        String reason = invalidAIUnitReason( aiUnit );
        return ( reason != null ) ? reason
                : ( ! canScoutNatives( aiUnit ) ) ? "unit-not-a-SCOUT"
                : null;
    }

    /**
     * Why is this mission invalid with a given colony target?
     *
     * @param aiUnit The <code>AIUnit</code> to check.
     * @param colony The potential target <code>Colony</code>.
     * @return A reason for mission invalidity, or null if none found.
     */
    private static String invalidColonyReason( AIUnit aiUnit, Colony colony )
    {
        return invalidTargetReason( colony, aiUnit.getUnit( ).getOwner( ) );
    }

    /**
     * Why is this mission invalid with a given native settlement target?
     *
     * @param aiUnit The <code>AIUnit</code> to check.
     * @param is The potential target <code>IndianSettlement</code>.
     * @return A reason for mission invalidity, or null if none found.
     */
    private static String invalidIndianSettlementReason( AIUnit aiUnit,
                                                         IndianSettlement is )
    {
        final Unit unit = aiUnit.getUnit( );
        final Player owner = unit.getOwner( );
        Tension tension;
        String reason = invalidTargetReason( is );
        return ( reason != null ) ? reason
                : ( is.hasScouted( owner ) )
                ? "settlement-scouted"
                : ( ( tension = is.getAlarm( owner ) ) != null
                && tension.getValue( ) >= Tension.Level.HATEFUL.getLimit( ) )
                ? "settlement-hateful"
                : null;
    }

    /**
     * Is this a valid scouting target because it is a suitable native
     * settlement or an intermediate colony.
     *
     * @param aiUnit The <code>AIUnit</code> to test.
     * @param settlement The <code>Settlement</code> to test.
     * @return A reason why the mission would be invalid, or null if none found.
     */
    private static String invalidSettlementReason( AIUnit aiUnit,
                                                   Settlement settlement )
    {
        return ( settlement instanceof Colony )
                ? invalidColonyReason( aiUnit, ( Colony ) settlement )
                : ( settlement instanceof IndianSettlement )
                ? invalidIndianSettlementReason( aiUnit, ( IndianSettlement ) settlement )
                : Mission.TARGETINVALID;
    }

    /**
     * Is this a valid scouting target because it is a suitable tile.
     *
     * @param aiUnit The <code>AIUnit</code> to test.
     * @param tile The <code>Tile</code> to test.
     * @return A reason why the mission would be invalid, or null if none found.
     */
    private static String invalidTileReason( AIUnit aiUnit, Tile tile )
    {
        return ( tile == null ) ? "tile-null"
                : ( tile.hasLostCityRumour( ) ) ? null
                : ( ! tile.isExploredBy( aiUnit.getUnit( ).getOwner( ) ) ) ? null
                : "explored-tile-lacks-rumour";
    }

    /**
     * Why would this mission be invalid with the given AI unit?
     *
     * @param aiUnit The <code>AIUnit</code> to check.
     * @return A reason for mission invalidity, or null if none found.
     */
    public static String invalidReason( AIUnit aiUnit )
    {
        return invalidMissionReason( aiUnit );
    }

    /**
     * Why would this mission be invalid with the given AI unit and location?
     *
     * @param aiUnit The <code>AIUnit</code> to check.
     * @param loc The <code>Location</code> to check.
     * @return A reason for invalidity, or null if none found.
     */
    public static String invalidReason( AIUnit aiUnit, Location loc )
    {
        String reason = invalidMissionReason( aiUnit );
        return ( reason != null )
                ? reason
                : ( loc instanceof Settlement )
                ? invalidSettlementReason( aiUnit, ( Settlement ) loc )
                : ( loc instanceof Tile )
                ? invalidTileReason( aiUnit, ( Tile ) loc )
                : Mission.TARGETINVALID;
    }


    // Implement Mission
    //   Inherit dispose, getTransportDestination, isOneTime

    /**
     * {@inheritDoc}
     */
    @Override
    public int getBaseTransportPriority( )
    {
        return NORMAL_TRANSPORT_PRIORITY;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Location getTarget( )
    {
        return this.target;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void setTarget( Location target )
    {
        if ( target == null
                || target instanceof Settlement || target instanceof Tile )
        {
            this.target = target;
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Location findTarget( )
    {
        return findTarget( getAIUnit( ), 20, true );
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public String invalidReason( )
    {
        return invalidReason( getAIUnit( ), getTarget( ) );
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Mission doMission( LogBuilder lb )
    {
        lb.add( tag );
        String reason = invalidReason( );
        if ( isTargetReason( reason ) )
        {
            return retargetMission( reason, lb );
        }
        else if ( reason != null )
        {
            return lbFail( lb, false, reason );
        }

        // Go to the target.
        final AIUnit aiUnit = getAIUnit( );
        final Unit unit = getUnit( );
        Direction d;
        Unit.MoveType mt = travelToTarget( getTarget( ),
                                           CostDeciders.avoidSettlementsAndBlockingUnits( ), lb );
        switch ( mt )
        {
            case MOVE: // Arrived at a colony
                break;

            case MOVE_HIGH_SEAS:
            case MOVE_NO_MOVES:
            case MOVE_NO_REPAIR:
            case MOVE_ILLEGAL:
                return lbWait( lb );

            case MOVE_NO_ACCESS_EMBARK:
                return this;

            case MOVE_NO_TILE:
                moveRandomly( tag, null );
                return lbDodge( lb );

            case ATTACK_UNIT:
                // Could be adjacent to the destination but it is
                // temporarily blocked by another unit.  Make a random
                // (directed if possible) move and try again.
                moveRandomly( tag, unit.getTile( )
                        .getDirection( getTarget( ).getTile( ) ) );
                return lbDodge( lb );

            case ENTER_INDIAN_SETTLEMENT_WITH_SCOUT:
                d = unit.getTile( ).getDirection( getTarget( ).getTile( ) );
                assert d != null;
                if ( AIMessage.askScoutSpeakToChief( aiUnit, d ) )
                {
                    lbDone( lb, true, "speak-with-chief at ", getTarget( ) );
                }
                else
                {
                    lbFail( lb, true, "unexpected failure to speak at ", getTarget( ) );
                }
                break;

            case EXPLORE_LOST_CITY_RUMOUR:
                d = unit.getTile( ).getDirection( getTarget( ).getTile( ) );
                assert d != null;
                if ( AIMessage.askMove( aiUnit, d ) )
                {
                    lbDone( lb, true, "explore at ", getTarget( ) );
                }
                else
                {
                    lbFail( lb, true, "unexpected failure at ", getTarget( ) );
                }
                break;

            default:
                return lbMove( lb, mt );
        }
        if ( unit.isDisposed( ) ) return this;

        // Retarget on failure or complete, but do not retarget from
        // one colony to another, just drop equipment and invalidate
        // the mission.
        lbAt( lb );
        Location completed = getTarget( );
        Location newTarget = findTarget( aiUnit, 20, false );
        if ( newTarget == null
                || ( completed instanceof Colony && newTarget == completed ) )
        {
            if ( completed instanceof Colony && canScoutNatives( aiUnit ) )
            {
                aiUnit.equipForRole( getSpecification( ).getDefaultRole( ) );
            }
            return lbFail( lb, false, ", found no targets" );
        }
        setTarget( newTarget );
        return lbRetarget( lb );
    }


    // Serialization

    private static final String TARGET_TAG = "target";


    /**
     * {@inheritDoc}
     */
    @Override
    protected void writeAttributes( FreeColXMLWriter xw ) throws XMLStreamException
    {
        super.writeAttributes( xw );

        if ( target != null )
        {
            xw.writeAttribute( TARGET_TAG, target.getId( ) );
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected void readAttributes( FreeColXMLReader xr ) throws XMLStreamException
    {
        super.readAttributes( xr );

        target = xr.getLocationAttribute( getGame( ), TARGET_TAG, false );
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public String getXMLTagName( ) { return getXMLElementTagName( ); }

    /**
     * Gets the tag name of the root element representing this object.
     *
     * @return "scoutingMission".
     */
    public static String getXMLElementTagName( )
    {
        return "scoutingMission";
    }
}
